It is known that active modulation of quantum layers by energy shifts and gain spectra is possible by applying the electric field across the quantum wells. For example, see Van Gleson, U.S. Pat. No. 4,700,353. Modulation of the semiconductor laser device is achieved at microwave frequencies by the application of transverse fields which produce energy shifts in the gain spectra of the laser diode. As described in the '353 patent, the laser device is a pn diode which has a body portion constructed from a non-conductive material, with p- and n-type implants on opposite sides. The p and n implants define a transition region, or layer, on the order of one micron in width, in which is formed a quantum well having a thickness on the order of 50 to 100 angstroms. Application of a bias voltage across the pn junction provides lasing of the device. An electrode on the surface of the transition layer allows application of a transverse electric field to the pn junction. This transverse field quenches the lasing of the device, to provide modulation of the laser.
The active region of the device disclosed in the '353 patent exhibits a change in gain characteristics due to the effects associated with quantum confined Stark effect. Essentially, an electric field applied across a quantum well spatially separates (in real space) the carrier, such that the overlap integral of the carrier wave functions and thus the optical gain is reduced. A significant disadvantage and limitation of the device described in the '353 patent is that only short pulses of energy can be extracted due to the short carrier lifetimes and small carrier populations.